I've noticed this in literature as well as the architecture of St Petersburg for example which resembles the architecture of Paris. I have also noticed that, living in an ex-eastern block state, a big portion of educated people of age 50+ are well versed in both French and Russian. Thus my question.
The intellectuals in Russia saw the French as the high point of refined European (Western) culture at the time. By the late 18th and 19th century, they saw themselves as a backwards peasant state and aspired to the cultural accomplishments of a nation like France, and as such French became a de facto intellectual language (as it was in other parts of Europe as well), and elites began to imitate aspects of French culture.
As a personal aside, I've always found that Russian writers FAR outstrip French writers of the 19th century when they are writing in a way that strikes me as distinctly contextualized in a Russian context. But maybe that's just because I'm sort of existential like that.
Interesting question, I'd like to know that too. BTW St Petersburg was built by Italian architects, so it's not specifically French I suppose.